1. Field of the Invention
The present invention relates to a focus detection method and a focus detection device for detecting a focus state from a contrast of a captured image.
2. Description of the Prior Art
A conventional digital camera with a contrast-detection type focus detection system which detects a focus state by performing a search operation in which a focusing lens group is moved from the infinite focus position (far extremity/position for bringing an object at infinity into focus) to the closest (shortest) focus position (near extremity/position for bringing an object at the shortest distance in working range into focus), or vice versa, is known in the art, wherein the search operation is terminated upon a peak contrast occurring during the search operation on the supposition that this position of the focusing lens group at which the peak contrast is obtained is an in-focus position. Furthermore, an invention is disclosed in Japanese Unexamined Patent Publication 2002-311325, wherein the search operation is terminated upon a plurality of peak contrasts being detected simultaneously at a plurality of focus detection areas, respectively, when the search operation is performed from the infinite focus position toward the closest focus position, and the search operation is terminated upon a peak contrast being detected at even one of the plurality of focus detection areas when the search operation is performed from the closest focus position toward the infinite focus position. Additionally, another invention is disclosed in Japanese Unexamined Patent Publication 2002-072074, wherein the search operation starts from the infinite focus position when the focusing lens group is positioned closer to the infinite focus position than the closest focus position, and starts from the closest focus position when the focusing lens group is positioned closer to the closest focus position than the infinite focus position, in order to reduce the time for the search operation.
However, in conventional focus detection systems, even if the search operation is performed from the closest focus position toward the infinite focus position, contrasts are detected by multi-pixel addition or the exposure time is extended when an object to be photographed is dark, and therefore, the search operation may be improperly terminated upon a false peak contrast being detected under the influence of contrast values outside of the selected focus detection area.